Said or thought by some people to be the stated bad or illegal thing, although you have no proof. (Cambridge Dictionary)
To say that someone has done something illegal or wrong without giving proof. (Cambridge Dictionary)
Accused but not proven or convicted. (Merriam – Webster)
Asserted to be true or to exist. (Merriam – Webster)
If you allege that something bad is true, you say it but do not prove it. (Collins Dictionary)
Said, without proof, to have taken place or to have a specified illegal or undesirable quality. (Oxford Dictionaries)
He was twenty seven, single an alleged part time student – the perfect type to drive such car. (John Grisham – The Runaway Jury)
Trump to get intelligence briefing on alleged Russian hacking.