Just the bare bones because I want to see the miriad ways you guys work out this plot.

A: There is a serial killer stalking Seatle (or wherever your campagin is set).

B: Lonestar is obviously offering a reward for his capture alive or dead.

C: A Corporation (you pick) is offering a much larger reward for him alive or dead and contacts the PC's.

One of the key questions of course is why is the Corp involved, especialy if the killer hasn't killed any of there people . . .

It's your typical Shadowrunner with a super bounty on his head because he acquired something sensitive belong to the corp, or else they ticked them off royally and they want him back for 'special purposes'. Somebody informed lone star before the corp could tell them not too, or else they're willing to 'rescue' them from prison afterwards.

Either way, bad news for the runner, but always fun to find out what goodies he picked up. And it's good to chase after other players if they keep the item, and the corp finds out.

My quick plot:

The corp involved got hold of some Berserker Chips in the Chaos surrounding the System Failure events and began trying to reverse engineer them in order to exploit the technology for a variety of purposes. The serial killer in question is actually one of their employees and for a myriad of reasons mostly relating to public relations, lawsuits, and the fact that the Corporate Court is still trying to locate and stamp out any Winternight Sleeper agents that might still exist. Putting the corp in an even more difficult spot is that the killer happens to be one of the top engineers on the project, while not the project manager a nearly irreplaceable technical mind, hence while Lonestar is putting a premium on dead the corp is putting a premium on captured alive. Of course once the man is captured the runners need to be prevented from disclosing what they know. Further twists could be offered in that the project manager might be a member of a radical group himself and is using the research as cover for other activities. If the killer hits some sort of VIP other teams or operatives may join the hunt. To make a complete cluster frag everyone finds the killer at once.

Some highly illegal black market personafix, one that modifies the users personality into a serial killer. Lone Star is offering the reward because even though they're corrupt they're still the police. The corp offers the reward because the technology originates in some secret and illegal test they did. Not that they produce BTL's but some new tech they did can be used for it. They either don't want the bad publicity, or they don't want their tech leaked.

The corporation made a line of personafix chips called "Lone Gunman", designed to make a single person into someone who would subsequently assassinate a third party specified by the program. The idea is that since the assassin would have nothing to do with the target or the corporation, success would be quite likely while deniability would be quite plausible.

Unfortunately, due to a handful of chips being mislabled as Bareback Mountain XVII: Dwarves in the Saddle, there are now a substantial number of assassins without explicitly specified targets. And now it looks like a frightfully efficient serial killer is on the loose.

The corporation has figured out how to remote shut-down all the chips (with commands imbedded in trid shows, like unto the bar scene in Serenity), but fears that unless the killings become "case closed" an investigation will eventually expose them, which will cost them a bundle in wrongful death settlements as well as completely undermining the deniability of future "Lone Gunmen" activities on their part.

So now the corporation wants to capture the culprit, so they can shut down all the other sleepers and have everyone involved call it a day. And if they could get a handle on how unassigned Lone Gunmen decided on a target that would be even better (which is why they would prefer one of the targets taken alive).

-Frank

1 - Add to Cold Dragon's suggestion: The serial killer is a runner paying back debts. His entire team was wiped out, he's getting payback. The corp wants him for the pay data as mentioned above.

2 - The serial killer is a top mage/engineer/researcher/son of an exec/otherwise valuable to the corp. He has a split personality usually controlled by drugs, but something went wrong (another corp trying to sabatoge their foe) and the evil personality came out. Complication - the evil personality is awakened, the main one is not, so even if the runners get data on him, they won't know he has magic on his side.

3 - If an experimental cyberzombie. Corp wants it back to figure out how it's still alive

I'm going to go a bit more classic than the above.

The serial killer is not a serial killer, per se at all. he/she is a shadowrunner. Said shadowrunner performed a very illegal, very underhanded and very dangerous run with his/her team and found out the truth about the run, resulting in said shadowrunner being the only one left alive.

Using vid evidence found in various ways, they "prove" that the shadowrunner is a serial killer (even though he/she is just killing on the way towards other things) so that they can go after the character in other corps/countries territories. The only problem is it leaked to Star, and they are after them to try and pin them with the law.

If the shadowrunner goes with Lone Star, they would likely blab their head off in an attempt to get life instead of the death penalty. Or maybe even lower the charges.

The corporation cannot take this chance, and so outsourced to try and get the shadowrunner before Lone Star.

The shadowrunner in the mean time is using his/her own contacts to try and pull their hoop out of the frying pan.

I would go with what Lord Ben and Frank Trollman have said: the serial killer is a high level / invaluable member of an R&D team that has been working on entirely illegal personfix chips for use in their "wetworks" department. Unfortunately one of the researchers actidentally loaded the persona and bugged out with the geekin'. Now both Lone Star and the corp want the culpret, the Star because the killer has been hitting rich areas of town and nothing gets them moving faster than rich humans complaining; the corp because they do not want their secret research to get out.

Twists:
The killer did not even load the chip. Rather after years of slogging through interview material and case loads of actual serial killers his mind finally broke (or maybe it always was broke). Now he's living out his fantasies without the aid of the chip, but is just letting the corp think the chip is affecting him just in case he gets caught.

Additionally, it could be neat to have each killing be a copy of a specific killing of a famous serial killer. The GM could add in some fun/unique details, possibly for anyone who took relevant Knowledge skills.

Very nice ideas all.

I'd make it this particular Corp's first attempt at a programmable stealth CyberZombie gone horribly wrong.

I never read any SR novels.

druids from the lord protectors office make a clone of someone in the royal family and put a "Jack the Ripper" persona fix on the clone. characters dont find out about it till after they finish operating, it was an attempt to discredit the british crown and it works.