In the murder of Stacey Burns, it may be stated as a fact that a conspiracy is in play. Is there a flaw in the following logic, and if, can you find it?

Given: Stacey Burns was murdered in cold blood by a amoral, sociopathic killer.

Given: Since there has not been an arrest, yet the police say that they know who the killer is, that killer must have an unshakeable physical alibi.

Given: If the killer has an unshakeable physical alibi, it must have been supplied by another person who would vouch for the killer’s whereabouts at the time of the murder.

Therefore: There must be two or more people involved in this murder– at the least, the killer and the person supplying the alibi to the police.

Does the old saying that two may keep a secret if one of them is dead apply here? I believe that someone knows Stacey Burns’s murderer, supplied an alibi for that killer, and is living with it on his/her conscience. Can two people who know the guilty party keep a secret?

I guess that remains to be seen but it surely has worked up to this point.