SAN FRANCISCO (KGO) -- A San Francisco mom is recovering from life-threatening brain injuries after someone attacked her while she was walking with her baby in Noe Valley. Doctors have asked the mother to avoid being overstimulated while her brain heals, so ABC7 spoke to her best friend, who was with her right before the attack.Surveillance video from a Nest cam shows the mother crossing 28th Street on Sanchez Street, around 6 in the evening, on Sunday, June 3rd. After she walks out of frame, you can hear her screaming and then 15 seconds later, her baby crying.The 37-year-old mother was walking home, carrying her 6-month-old when she got a call from someone, who is now an important witness."My friend was on Facetime with her sister, then her sister heard my friend say 'he hit me'," explained Jess Farb, who is best friends with the mother.They were playing with their daughters at Farb's home in Noe Valley, before the attack. Farb says based on the CT scan, doctors believe the attacker hit her friend on the head with a blunt object, like a hammer. "She had severe skull fractures and pieces of her skull entered her brain, so that night she had to have emergency brain surgery."In the surveillance video, after the mother crosses the street, you can see a person in dark clothing carrying something, moving quickly down the street and around the corner. Ten seconds later, when you hear the mother scream, you can see another person running up the hill.So far, this is the best-known surveillance of the incident. On Thursday, friends of the family, from all over the Bay Area, spent the evening canvassing the neighborhood with flyers, looking for more evidence.The motive for the attack is unclear, but Farb hopes people in the neighborhood will remain extra vigilant, "it had to have been someone out of their mind who could commit a crime like this. I don't think any straight thinking person could do this."SFPD says this is still an active investigation and that they are also still looking for more video and witnesses.The victim's husband tells ABC7 that his wife is healing at home and they are grateful for the outpouring of support.Investigators have canvassed the area, but they are asking anyone who lives in the area to check their home or business surveillance systems for any images that they feel might be useful.