Sometimes, the situations people get themselves into never ceases to amaze me.
For example, often, when a murderer is brought to trial, they drag other people down with them. And those other people often seem surprised a murderer could do that to them, even though they may suspect that person had killed someone just because they found it necessary. When a guilty verdict comes in, people who supported murderers can find themselves forever tainted by a murder they had nothing whatsoever to do with. What they had done though, was support a story of a stay-at-home day, an outfit worn/not worn, a car not driven or maybe a phone call that wasn't what it seemed.
And there you are. Somebody has died, police are investigating, life sentences - even death sentences - are in the air, media are making sure your role will be remembered for a long, long time to come.....and you decide it's a good decision to tell a little lie.
I don't think it matters if the person is ever prosecuted or not, or serves time - just imagine being tainted by a murder because you chose to tell a tiny lie about someone watching a TV program with you when they weren't actually in the house, for example. Especially if murdering someone was the last thing that would ever cross your mind. It can only be done when people try and put six degrees of separation between themselves and the crime that may have been committed, imo.
People who would easily send a slightly dodgy salesman at the door packing have accepted the most incredible reasons from murderers about why they should lie, and gone ahead and lied for that murderer.
I'm not saying it's happened in Bob's case. Just saying it often does. And those people almost always regret it. Some of them even speak out with the truth, just in time to save themselves; usually when they finally come to the conclusion most murderers are better equipped than most, to look after number one first.