Police investigating the murder of Daniel Young near Morden station made a second arrest on Thursday evening.
Young, who had just started a new job as a teaching fellow at Coventry University's London Campus, was stabbed to death around 8am on Tuesday as he walked through Kendor Gardens to access the tube, on what would have been his second day at work.
The 30-year-old died at the scene from stab wounds despite one passer-by desperately trying to save him by performing CPR.
A 26-year-old man was initially arrested on suspicion of wasting police time, but was subsequently arrested on suspicion of murder. He has been bailed until a later date.
Police have now said they have charged a 35-year-old man on suspicion of murder. He remains in custody at a south London police station.
A post mortem has now been completed on Young and established that his cause of death was stab wounds. Police have refused to discuss where on the body Young was stabbed.
Police are yet to establish a motive for the murder, saying they are keeping an open mind as to whether Young was attacked by a stranger or someone known to him.
Detective Superintendent Paul Monk said: “I understand the concerns of the public and particularly the residents of Merton, that the attack on Daniel Young was unprovoked and potentially committed by a stranger in a random attack.
“We too share those concerns and have allocated significant resources to find the person who did this.
“I reiterate that random attacks of this nature are thankfully rare in London, however, we keep an open mind and at this early stage are not ruling out any line of enquiry.”
Earlier this week it was thought police were investigating a possible link between Young's murder and another stabbing that occurred 45 minutes earlier a short distance away. A 23-year-old man had been stabbed in the buttocks on Lewis Road, around half a mile away from the murder scene, about 45 minutes earlier.
Police said the two incidents have not been linked, but detectives are working to establish if there is any evidence to suggest the same suspect committed both attacks.
Detective Chief Inspector Cliff Lyons on Wednesday appealed for anyone who witnessed the attack on Young - who was believed to have been stabbed multiple times - to come forward.
Lyons said Young was stabbed during rush hour when a large number of commuters were making their way to and from the tube and appealed for any witnesses to the attack to contact police.
"I am appealing for anyone who may have seen the stabbing or the events leading up to the incident to get in contact with us.
"I believe that suspect would have entered and exited Kendor Gardens via Dorset Road and Kenley Road. From which direction they entered and exited has yet to be established.
"I would like to hear from anyone who was in or around the Kendor Gardens area between 07:50hrs and 08:15hrs who can help with establishing the movements of the suspect."