During the course of the trial, jurors heard evidence from Mrs Groce's son Lee Lawrence - aged 11 at the time of the shooting - who watched his mother being shot by police.
More top news
The killer's solicitor has written to police challenging them to prove his confession.
Tottenham last won the league back in 1961 - but they are feeling confident after a string of great performances this year so far.
Crimestoppers are offering the reward as police say they are becoming increasingly concerned at the viciousness of the assaults.