Alice, 14, from Hanwell, west London, went missing on August 28 and her body was recovered from the River Brent in west London on Tuesday.
Police believe a badly decomposed body found on Saturday in dense woodland in Boston Manor Park, west London, is that of Zalkalns.
A Scotland Yard spokesman said: “We can now confirm the body has now been recovered by specialist officers and taken to a west London mortuary. A post-mortem examination will be held in due course.”
Scotland Yard said yesterday that although no formal identification had been made, “early indications suggest the body may be that of Arnis Zalkalns. We have updated his partner and a family liaison officer is supporting her”.
According to reports, the dead man was found hanged.
Police stood guard at all entrances to the large park last night and told people wanting to enter that it was closed.
Officers could be seen walking inside the park, particularly under the M4 flyover at the Brentford end of the park, and a forensics van could be seen.
Zalkalns had been spotted following Alice along a canal towpath. The 41-year-old convicted killer has been missing since September 3.
Alice was last seen on CCTV walking beside the Grand Union Canal near her home on the afternoon of August 28.
Nearly three weeks later investigators realised that Zalkalns, who was reported missing by his family on September 5, had been cycling behind her.
He served seven years in prison in his native country for bludgeoning and stabbing his wife Rudite to death.
The general labourer, who worked at a building site in Isleworth, west London, is believed to have come to the UK in 2007, but authorities here are thought to have had no record of his murder conviction.
The Metropolitan Police have come under fire for delays in identifying Zalkalns as a suspect.
The police spokesman said: “Although Arnis Zalkalns had been identified as a suspect in the Alice Gross murder investigation, inquiries continue to establish the full circumstances surrounding this crime. Officers are still searching for evidence.”