Memphis - Sheriff's deputies have found a large butcher's knife with what appeared to be blood on it in an apartment where a Tennessee mother killed her four children by cutting their throats, court documents say.Shanynthia Gardner, 29, of Memphis, has been charged with four counts of first degree murder while committing aggravated child neglect in the deaths of her three daughters and one son - all under the age of 5. Their bodies were found after deputies entered her apartment in a gated community in unincorporated Shelby County on Friday. Neighbours and friends of the family attended a vigil to honour the victims on Saturday.Gardner also faces four counts of first degree murder while committing aggravated child abuse; four counts of aggravated child neglect or endangerment; and four counts of aggravated child abuse. She is being held without bond, with an arraignment scheduled for Tuesday.An affidavit filed in Shelby County court by a sheriff's detective identified the victims as 4-year-old Tallen Gardner; 3-year-old Sya Gardner; 2 year-old Sahvi Gardner; and 6-month old Yahzi Gardner. A fifth child, 7-year-old Dallen Clayton, fled the apartment and escaped the attack, the affidavit said. Dallen is Gardner's son from a previous marriage.Gardner spoke by phone with her current husband, Martin Gardner, and acknowledged that she killed her children, the affidavit said. Attempts to reach him or relatives of the Gardners have been unsuccessful."This is a terrible act, an egregious act that has shocked, I believe, the community, and has shocked our staff to the core," Shelby County Sheriff Bill Oldham said on Saturday.Deputies were called to an apartment complex in unincorporated Shelby County on Friday afternoon. When they arrived at Shanynthia Gardner's apartment, they found her with superficial cuts to her neck and wrists, the affidavit said. Deputies also found four children with "severe lacerations to the throat," the document said.Two children were found in the living room - Yahzi was in her baby carrier and Sya was lying next to the carrier. The other two victims were in a bedroom.Mental problems The affidavit said Dallen was able to escape the apartment and run up to a man, yelling that his mother had stabbed his sister.The man told officers that he saw Shanynthia Gardner come outside with a large knife in her hand, then re-enter the residence. Deputies found the knife in the apartment, the affidavit said.Authorities have not divulged what circumstances they believe led to the killings. Oldham said investigators were trying to determine if Gardner has mental health problems.In March 2015, Gardner disappeared briefly after leaving work early and picking up her children, according to a Memphis police report.According to The Commercial Appeal, her husband told police she was having problems at work and feeling anxious, and "she also has been feeling that someone is trying to harm her and her family", the report said. She called her husband that night from Corinth, Mississippi, and she later was found at a Memphis hospital emergency room.The state Department of Children's Service has offered its assistance to local law enforcement, but has no record of interaction with the slain children, said spokesperson Rob Johnson.About 30 people attended an outdoor candlelight vigil at the apartment complex on Saturday evening. They prayed for the four children, the surviving boy, and Shanynthia Gardner. A pastor poured water from a decanter onto the ground, in remembrance of the victims.'Work of the devil'Sonya Clayton, Dallen Clayton's grandmother, said she had not seen the boy's mother for a few years. She said she was shocked by the attack."She was a sweet young lady," Clayton said of Shanynthia Gardner. "What happened, I don't understand."Later, Sonya Clayton said she forgives her former daughter-in-law."I know this is the work of the devil," Sonya Clayton said. "I know this is not Shanynthia. And I pray and I love Shanynthia."Sonya Clayton said her son, Detrail Clayton, has not seen Dallen since the stabbings. She said her son is not doing well, and he wants to see Dallen soon. Sheriff's officials say the boy has been under protective supervision.Neighbour Mona Hansen, who attended the vigil, became emotional when talking about how her own daughter adopted three girls after their brother was killed by a parent. Hansen called the killings of the four children in the apartment complex where she lives "heart-wrenching"."Like the minister said, you don't know what they could have been in life," Hansen said of the Gardner children. "Their lives didn't even get started yet, before they were taken."