The night my son was born, my Evil Brother-In-Law had talked my husband into going to a car race in a nearby town despite my intuition that the baby would come sooner than the projected date two weeks from then. I reminded them that our first was born quickly so maybe it wasn't a good time to be gone from home, but no, they had to go anyway.
Naturally, I went into labor an hour after they left, and called the stadium where the car race was and had my husband paged. My miserable brother-in-law answered the phone instead, and I told him to get home "now", the baby was coming forthwith. He assured me that I was no doubt having false labor, ("Just relax, it'll take hours before anything happens"). He failed to convey the urgency of the message to my husband, and they lollygagged and arrived several hours later (traffic, you know), by which time our son was already born.
This happened in 1970, and I barely spoke to my brother-in-law for years. My husband flees the room to this day if he thinks I am going to bring it up.
Anyway, I can attest that guys do weird, out of the norm things when babies are due(my husband had never been to a car race and never went out without me, so it was very unusual). These types of events are designed to give wives things to hold over their spouses for infinity, so there is an upside.
Seriously, without more evidence, of course we can't assume the guy killed his wife because he went fishing, though he is the statistically most likely person to have done it.