When Tasha and Jane are shot loud gunshots are heard. When the shooter appears moments later his gun has a silencer.
When Vince, Frankie and Nina arrive at the Grant St buildings, Frankie rushes through a door that was locked when Jane tried it minutes earlier.
When Jane hands Tasha the phone to talk to Maura, the phone is upside down. Meaning the cord is facing up and Tasha would have been talking into the earpiece instead of the mouthpiece. Next shot of Tasha with the phone it's in the correct position.
It's never explained how the shooter knew there was a witness, or how he found where she was hiding.
At the end Maura says "You did good Jane". However, "good" is an an adjective, and a pedant like Maura would certainly have used the appropriate adverb: "You did well".