WHYY By Philadelphia Police Commissioner Danielle Outlaw speaks at Olney Transportation Center, where a mass shooting occurred on Feb. 17, 2021. (Emma Lee/WHYY) City prosecutors and police stood inside a cavernous West Philadelphia church earlier this month to announce that four men now face criminal charges for allegedly injuring nine people, including three children, in a series of retaliatory shootings in 2018 and 2019. The charges stemmed from a lengthy grand jury process. Police Commissioner Danielle Outlaw credited ballistics evidence, cell phone records, and surveillance footage. She said evidence culled from social media also proved to be “invaluable” to the investigation launched under the umbrella of the city’s Gun Violence Task Force.