[0xmohit]

I buy a gun. Lend [0] it to friend. Friend goes on a killer spree.

Can I claim zero responsibility? No.

[0] The friend didn't steal the gun.

[LyndsySimon]

Legally, in most US states... it would be a stretch. The prosecutor would have to prove that the lender reasonably expected their friend to commit the crime.

FWIW, I've lent firearms to people on multiple occasions, sometimes for months or years at a stretch.