Ten Things You Need to Know Today: Monday 17 Dec 2012

President Obama promised to use all his powers to prevent repeats of the Sandy Hook primary school massacre of 20 children and seven adults when he attended an inter-faith service at the site in Connecticut last night. "These tragedies have to end,"he said."And to end them we must change." A gun control bill will be launched in Congress this week, but its chances of success are deemed low.

A police constable with the diplomatic protection group SO6 has been arrested on suspicion of misconduct in a public office, the Met Police said last night. The officer is accused of leaking the police log recording the Downing Street "plebs" row which led to the resignation of Conservative Chief Whip Andrew Mitchell.

Fifty-eight dissenting MPs and peers, including 35 Conservatives, have signed a letter in today's Daily Telegraph opposing the government's plans to legalise same-sex marriage, claiming that the government "does not have a mandate to redefine marriage". The letter says that at the last election"none of the three main parties stood on a platform to redefine marriage".

Former Italian PM Silvio Berlusconi, 76, who is facing charges of paying an underage girl for sex, says he has become engaged to 27-year-old Francesca Pascale, seen on his arm since he announced that he would run for office again next year. She makes him "feel less lonely". But Berlusconi has yet to reach divorce terms with his current wife, Veronica Lario.

A leading Palestinian official has said Tony Blair’s role at the Office of the Quartet Representative in Jerusalem is "useless, useless, useless". Mohammed Shtayyeh, an aide to the Palestinian President Mahmoud Abbas, said the Quartet's work "took us to nowhere".