The SIS is a highly specialized unit within LAPD that handles surveillance of suspects. The team is very good at what it does, but it also had a high kill rate. This is probably due in large part to the fact that the team is watching serious criminals who are not in custody and don't know they are being watched. It is not surprising that these law breakers would be observed engaging in a criminal activity and that they would respond violently in order to avoid arrest. The SIS would be in a position to be the first responders.
In 2010 the unit was headed by Lt. Stephen Wright. He has been in the unit for 20 years and is a master of surveillance. It helps that he doesn't look like a cop. In February 2010 SIS was assigned to follow and observe Jason Jessup during his retrial for the murder of Melissa Landy. Daily reports were given to detective Harry Bosch.
On 8 April SIS officer Manuel Branson was killed by Jason Jessup, highlighting the dangerous nature of the job. Later that day SIS officers located Jessup in his hiding place under the Santa Monica Pier. They gave him an opportunity to surrender, which he did not. When they entered the space where Jessup was hiding, he fired first and SIS returned fire, killing Jessup.