SA murder suspect was pen pal with victim

A Victorian man who is the prime suspect in three separate cold-case murders in South Australia was a pen pal with one of the victims, her family says.

Grandmother Beverley Hanley was warned by her family about having contact with Steven Hainsworth before she was killed at her Elizabeth North home in 2010.

"I was at grandma's house not long before she died. I found a letter on her kitchen table from him saying when he got out of jail he was going to be a changed man," granddaughter Tasha Chase told News Corp on Friday.