The family of a boy stabbed to death with a friend have launched a Downing Street website petition calling for his killer's sentence to be increased.
Thomas Palmer was sentenced to serve at least 20 years
Nuttawut Meechao, 14, and Steven Bayliss, 16, were killed by Thomas Palmer, 18, in Barkham, Berkshire.
The attorney general has already ruled that Palmer's 20-year sentence was not unduly lenient enough to be reviewed.
But the family of Nuttawut are now petitioning the prime minister to order a review of the minimum tariff.
Gerald Pontet, guardian of Nuttawut, who was known as T.Wood Nadauld, said: "Thomas Palmer was given a life sentence for the double murder of T.Wood Nadauld and Steven Bayliss which, although was within the sentencing guidelines, was at the very lower end of those guidelines.
"The attorney general has refused to review the sentence. Only public opinion can force him to reconsider."
Palmer stabbed the pair of teenagers with a hunting knife in woods near Finchampstead in September 2005.
He was jailed for life at Reading Crown Court in March with the tariff set at 20 years.