Catholic priests are required to observe the
Liturgy of the Hours, which means daily prayers said at particular times of the day. Vespers, or the evening prayer, is said between about 4 pm and 6 pm, generally. They don't have to say these prayers in church, but many do. Also, from what I've observed over the years, when priests pray in church, they often choose a pew in a quiet corner either off to the side, or in the very back of the church. It just seems like the housekeeper would have recognized the priest even in the semi-darkness, but perhaps she had poor eyesight. Or she lied. I wonder if the detectives asked her about the priest's routine.
What always sticks with me is the very short window of time in which the crime occurred. It's too short, imo, with the housekeeper, cat, bank teller, friends, and a praying man coming and going, for a perpetrator to have gone unnoticed. How did that praying man not see him? Or not see CA? Even if he didn't, if he were a parishioner, or just a local, wouldn't he have come forward to say he was in the church around the time of the crime? Yet, I've never read where LE identified him, or questioned him.
On the other hand, for some reason the man was moved to go to church on a weekday afternoon. The housekeeper said he was praying, on his knees in prayer. It's hard to picture this same man, in the middle of his prayers, suddenly being overtaken by an impulse to rape and strangle a little girl who wandered in. It's easier to imagine a less than devout priest, for whom daily prayers said over and over for years have become drudgery, so that even while going through the motions, his heart and mind are elsewhere. Also, the man must have seen the housekeeper. If were a local in this small community, wouldn't he have been concerned that the housekeeper would identify him?
Whoever was the attacker, I agree he had to be very familiar with the surroundings. A parishioner might be comfortable enough to latch the front door and follow CA up the stairs, but there was another door a parishioner couldn't secure, and that left him vulnerable. If someone walked in, there was no way he'd escape without being identified. I'd think to take such a tremendous risk, the man would have to be certain the priest would not enter through the sacristy, and no one could be that sure except the priest, himself.
ETA: Image of the church interior is from this link,
http://www.pahrc.net/index.php/2011/04/