You're likely referring to the ATF gunwalking scandal[0], the best known piece of which was "Operation Fast and Furious"[1]:
[0] https://en.wikipedia.org/wiki/ATF_gunwalking_scandal
[1] https://www.cnn.com/2013/08/27/world/americas/operation-fast...
You are thinking of Operation Fast and Furious I believe.
Entrapment _generally_ requires more than that law enforcement facilitated the crime: it (broadly) requires that they somehow induced someone to commit a crime they would otherwise be unwilling to.
Given the facts in the article that Morley is the likely bombmaker, knew the brothers, and the feds particularly the FBI are protecting him, it now appears that the Marathon bombing was yet another terror plot thought up by the FBI, Morley was working under their direction and was their handler, and the FBI lost control of the situation in this case and failed to execute the arrest before the bomb was actually deployed.
https://www.globalresearch.ca/the-boston-bombings-and-the-ci...
“Ruslan Tsarnaev, the outspoken uncle of the brothers was married to Samantha A. Fuller until 2004. Samantha’s father is Graham Fuller, the senior CIA person who was the architect the Afghan Islamic fundamentalist Mujahideen war against the Soviets.”