The tall and well built Killen offers significant presence to a powerfully built forward line alongside the likes of Rory Fallon and Chris Wood, and provides a regular target for the All Whites on set pieces.

Since making his debut at the 2000 OFC Nations Cup, Killen has built up an impressive scoring rate but until recently he made only spasmodic appearances for the national team, playing just one match in the Oceania zone of FIFA World Cup™ qualifying. Since then however Killen has been regularly selected and scored a brace against world champions Italy in a lead-up match just prior to the FIFA Confederations Cup South Africa 2009. He then featured heavily in all three of New Zealand’s matches at South Africa 2009. Killen was also a notable presence in the intercontinental playoff victory over Bahrain which ensured New Zealand’s qualification.

Indicative of Killen’s value at national team level was his inclusion two years ago in the New Zealand U-23 squad for the nation's first appearance at an Olympic Games football tournament as one of three over-age players, alongside All Whites icons Ryan Nelsen and Simon Elliott.

Killen has spent his entire club career in the United Kingdom, firstly with Manchester City before a productive four-year stint at Oldham was followed by an equally productive, albeit briefer stint with Hibernian. In a surprise move Killen joined Celtic in 2007 but he found a starting berth harder to come by, resulting in a loan move to Norwich City. Earlier this year he followed former Bhoys manager Gordon Strachan to English Championship side Middlesbrough where he has since enjoyed regular first-team action.