Responsibility for the attack has not yet been claimed, but senior politicians are pointing towards dissident republicans who oppose the power-sharing peace process.
Northern Ireland First Minister Peter Robinson described the attack as a "Neanderthal" attempt to scare Catholics from joining the province's police service. British Prime Minsiter David Cameron said those who carried out the crime would not be allowed to drag Northern Ireland back to a "dark and bloody past".
Kerr, who only completed his training three weeks ago, is the second member of the PSNI to be killed since 2001, The first was shot dead during an outbreak of deadly attacks by dissidents in March 2009 that also saw two British soliders gunned down.
The Northern Ireland Assembly dissolved last week ahead of elections to be held on 5 May. It was the first time the devolved power-sharing administration had completed a full four-year term.
Meanwhile, the threat level for Northern Ireland, set by Britain's Home Office interior ministry, is at the second-highest of five levels indicating that an attack is considered highly likely.
The Independent Monitoring Commission which tracks paramilitary activity, said in a report last November that dissident groups continue to pose "a substantial and potentially lethal threat, particularly against members of the security forces".