Lets assume that someone has a SIN which, for whatever reason, he wants to keep more or less clean instead of ditching it. And to throw off any investigation, or at least slow them down, he wants to create one or more alibis which proof that he (or rather this SIN) was in no way involved in those Shadowruns everything is speaking about.
What good ways are there to do this?

The most easy way would be to have an agent or friend surf the matrix when you are running, buying stuff you would buy according to the buy history of the SIN or visit a location you would plausibly visit and spend some money there. But any investigators would know how easily that is faked so it is a rather weak alibi.

A harder one would have a double of you walking around, broadcasting the SIN like a good citizen and do whatever you would do (hopefully buying stuff so there are more logs of your SIN floating around). A physical disguise is a must so that all camera logs confirm that it was really you doing this stuff. If you already have more persistent investigators on your tail it might even be necessary to "accidentally" cut yourself or otherwise lose some prepared ritual sample. Just be sure you already have switched places when they have time to use it. If they don't use it to aid their investigations you have the problem that they now can perform a ritual sample which they can use any time they want.

In my opinion, faking all this by hacking is hard. It might fool a low level investigation when you place some records of SIN activity in databases (I think it would be quite effective to place those logs into the databases of the organization which is investigating you, like a small fine for loitering or speeding inside the KE databases. Its one thing to mistrust foreign data, but your own? The downside is that its much easier to check if the record is true, so make sure that the cameras have recorded you and that the involved people remember the correct thing.)
Speaking of cameras, they are imo the biggest problem with hacking an alibi. Sure, you can fake a recording of you standing in the store and buying something at the time you have inserted into the database. But what about the dozens of cameras which would have picked you up when entering or leaving the store and the hundreds of them between the store and the parking garage? You can't hack all of those recordings.

Does anyone else have a genius idea how to create an alibi?

Cameras can be fooled by going to really crowded places. You can make it hard for your face to be picked out. Also, there's no way they'll run facial recognition on everyone in a crowd, so if you have someone who generally matches your look and metatype, that should be all right.

Of course, none of this matters if your fake SIN is cracked. And since SINner is a negative quality, I wouldn't let players get away with handing a real SIN to an accomplice. Really, your best ally is anonymity. The less you have on record, the more you'll get away with.

If you want to protect a particular fake SIN, just don't use it. By RAW, an inactive SIN can't be cracked, so you can keep backup identities in storage.

Datatrail alibis are unreliable at best – data has never been less trusted on sight and if you're under suspicion of shadowrunning then it's likely you or a buddy know a thing or two about hacking. And if the data is found to be planted then it's a sure sign of guilt.

People are better – if a reputable cop will put his badge on the line to place you across town receiving a verbal warning or a corporate judge says he had an off-the-books meeting with you all night then a hell of a lot of cirumstantial evidence will get waived. The trick is offering the right bribe/threat to the right people.

Physical mask + some one you trust using your ID/commlink = pretty good alibi. Also, already have a lawyer.
IRL criminals with good lawyers don't even go to trial unless the prosecution is really sure they did it and have really really good evidence. And even then, a lot of times that good lawyer will get enough evidence tossed that the cops can't even get an indictment, much less a conviction.

My thoughts exactly. I would add wearing a rubber mask of myself on runs which you can occasionally leave behind:

"See, officer, these crooks chose my face out the blue for their heinous crimes! They are framing me!"