Lawyers are arguing a key identification of Scott Watson is unreliable

The 52-year-old who's in jail for murdering Olivia Hope and Ben Smart in 1998, is making his second attempt before the Court of Appeal this week.

The defence claims police used moral pressure to get a key witness to identify Watson in it's final submission.

Herald reporter Melissa Nightingale says it's a long process.

She says it's going to take days for both sides to deliver their submissions.