As reported in the Washington Post…

Finally discovered, the Tsarnaevs led police on a chase through residential streets, hurling grenades and makeshift bombs as they drove. When cornered, they battled police with guns and more homemade explosives, wounding a transit officer and trading more than 200 rounds until the officers ran out of ammunition.

If they only had to reload at shot number 15…

And, wtf?  Officers ran out of ammunition?  This is how the NRA is ruining America.  Give Criminals more rights than have the police…   (That and shooting defenseless pigeons in boxes…. )