West Midlands Police said they have recovered two motorbikes which they are now forensically examining.
A 14-year-old boy who was arrested on suspicion of causing death by dangerous driving after a seven-year-old died following a motorbike collision has been released on bail “with strict conditions”, police said.
Katniss Seleznev was killed in the crash in Walsall just after 7pm on Thursday, West Midlands Police said.
The girl was found with critical injuries and was taken to Birmingham Children’s Hospital but later died.
Officers said they have found two abandoned motorbikes which will now be forensically examined.
Detective Sergeant Paul Hughes, from the Serious Collision Investigation Unit, said: “Our work to establish the facts around this tragic incident is continuing.
“We have recovered two motorbikes and they will now be forensically examined as part of those extensive inquiries.
“And at this awful time our thoughts remain with the family of Katniss, who are being supported and have asked to be left to grieve in private.”
Flowers, balloons and stuffed toys were left at the scene of the crash on Friday.
Dozens of bunches of brightly-coloured bouquets paid tribute to the girl, with one reading: “I will remember your beautiful soul forever. Thinking and praying for your family.”
Another said: “Rest in peace beautiful girl.”
A steady stream of emotional people had been visiting the scene to add their own tributes and comfort each other.
In a Facebook post, her mother said that her “heart is bleeding”, adding: “God took her away too young and fragile.
“I don’t have strength and I don’t want to say goodbye to you, my star.
“How to let you go, my heart is bleeding, my soul is aching.”
Mr Hughes said: “I would also like to extend my thanks to all those people who have already come to us with information, it is truly appreciated.
“We would ask again that anyone who was at the scene does still come forward, as what they know may be valuable to our ongoing investigation.”