This is how reliable BD's accounts were - we know Avery had the cut prior to the disappearence of Teresa however .....
WIEGERT Did you notice any marks on Steven at all?
BRENDAN On his arm.
WIEGERT Where on his arm?
BRENDAN Like right here.
WIEGERT Do you remember which arm?
BRENDAN His left.
WIEGERT His left arm? OK. I’m sorry. I’m gonna keep tellin’ you to speak up a How did he get that mark?
BRENDAN Well, he said that he got it from workin’ out by the yard, that he cut OK.
WIEGERT Did he tell you anything else about that mark?
BRENDAN No.
WIEGERT Did he tell you that at any time that he had been injured when he had killed Teresa?
BRENDAN N-no. That he got a scratch, I think.
WIEGERT Where was that scratch?
BRENDAN Like on his finger
WIEGERT OK. How did he say he got that scratch?
BRENDAN That from a fingernail or somethin’.
WIEGERT: Did he tell you that?
BRENDAN: Yeah.
WIEGERT: So tell me again exactly what he told you.
BRENDAN: That he got it from someone scratched, someone scratchin’ um.
WIEGERT: Did he tell you who? Scratched him?
BRENDAN: Teresa.
WIEGERT: How did that come about? I mean did he say was there a struggle or something? Or what did he say?
BRENDAN: Yeah, there was a struggle.
WIEGERT: Tell me about that. What did he tell you?
BRENDAN: When he was trying to tie her up, she tried to get out and scratched ‘em tryin* to get away from ‘em and she couldn’t so he tied her up and stabbed her.
WIEGERT: Did he say anything about that? Did he say if she was yelling or screaming or anything? Did he say
BRENDAN: No.
WIEGERT: So, he actually showed you the finger?
BRENDAN: Yeah.
WIEGERT: And which finger was it?
BRENDAN: The pointer finger.
WIEGERT: Did you see anything on that finger?
BRENDAN: Yeah, a scratch.
It's also easy to see how BD is open to suggestion, something picked up on during his psychological examination.