Former NFL player Sergio Brown appeared to post on social media two days after his mother’s body was found in a creek behind her home in Illinois. The Maywood Police Department said an investigation is underway into the death of 73-year-old Myrtle Brown after it was determined that she was murdered. Authorities have yet to locate Mr Brown, who was reported missing along with his slain mother after they failed to answer calls from family members. On Tuesday evening, an account linked to Mr Brown made a second post on Instagram stories referencing the movie Finding Nemo. Mr Brown is seen rambling and laughing on the post. He also appears to be mocking reports that he is “missing.” “Just keep swimming. Missing? What the f*** is going on?” he is heard saying. The former NFL star had previously posted another story showing erratic behaviour and claiming he had been kidnapped by law enforcement. “I thought my f****** mama was on vacation in Sinaloa. That’s f****** fake news,” he said. “Get the f*** out of my goddamn face. She’s retired, and you want to come to me? The FBI had to do it. They have some power to do some s*** like that. What the f*** is going on? That’s fake news.” Relatives of Mr Brown and his mother contacted authorities on Saturday after they couldn’t get in touch with them for over 72 hours. Myrtle’s sister Sheila Simmons told WGN-TV that she had last spoken with her on 14 September and neither she nor Mr Brown were answering calls. The Maywood Police Department then launched a missing persons investigation. Later on Sunday, family members and authorities found Myrtle’s dead body in the Addison Creek Reservoir, less than 100 yards from her home. The Cook County Cook County Medical Examiner’s Office confirmed Myrtle’s death was a homicide. According to records obtained by WGTV, she died from multiple unspecified assault injuries. “We’re going to find out what happened because it’s not normal for my sister to not answer her phone, not to respond to text messages,” Ms Simmons told the outlet about her sister’s death. “People have been reaching out to her since Friday. No one was able to reach her. Now, I got the call this morning saying that she’s missing, so immediately I came out here and find out my sister is dead.” Carlos Cortez, a neighbour of Myrtle Brown’s, told WBBM that family members had told him Mr Brown had not been acting like himself lately but did not elaborate on what type of behaviour had given that impression. “They said he wasn’t himself the last few months. He was out of his mind,” Mr Cortez told the outlet. Mr Cortex also said that he had given authorities Ring doorbell video, in which Mr Brown is reportedly seen burning his mother’s clothes. The Maywood Police Department declined to comment on the allegations when reached out by The Independent. Anyone with information regarding Myrtle Brown’s murder or Sergio Brown’s whereabouts is asked to contact the Maywood Police Department Anonymous Tip Line at 708-450-1787. Read More Missing ex-NFL player Sergio Brown ‘posts video rant’ on Instagram after mother found dead: Latest updates Missing ex-NFL star posts bizarre Instagram about police and FBI after mother found dead in creek Ex-NFL star Sergio Brown and his mother went missing. Police say she was murdered and he has yet to be found