A German sniper was sentenced to 20 years behind bars Thursday for joining a squadron of elite mercenaries who called murders-for-hire “ninja work” and plotting to assassinate a federal DEA agent.

Dennis “Nico” Gogel pleaded guilty in January in Manhattan federal court to conspiring to murder the agent and a confidential informant in Liberia for $800,000.

Gogel — who faced a sentence of up to 28 years in prison under his deal with the feds — also confessed to other crimes, including attempting to import cocaine and possessing machine guns with silencers.

“How stupid I feel to have engaged in something like that,” Gogel said at his sentencing.

“I’m not the same person I was before.”

When the ex-US Army sergeant who organized the mercenary crew wrote to Gogel in 2013 to confirm he understood the nature of the work they would do, Gogel responded whole-heartedly.

“I understood: I was recruited by an sniper instructor wich I meets in Iraq … I full understand what ‘Ninja’ means and I m available for your request!” Gogel wrote, according to court papers.