"report has concluded" is correct and can be used in written English.
It is usually used as a summation of a process or discussion, to indicate that the report has been completed. For example: The independent investigation into the scandal has concluded, and the report has concluded that the company was at fault.
A Second World War Spitfire crashed after landing when its pilot pulled the wrong lever, an accident report has concluded.
A runaway train sped out of control for almost five miles after its brakes were damaged, a report has concluded.
Though most women were killed before they could tell their stories, a U.N. report has concluded that at least 250,000 women were raped during the genocide.
Putting a major road past Stonehenge into a tunnel could benefit the world heritage site if the scheme is well designed and constructed, an international report has concluded.
The UK is shirking its responsibility to care for thousands of unaccompanied migrant children, dismissing them as "somebody else's problem", a report has concluded.
The international news channels broke the rules on sponsorship and current affairs programming almost 50 times between 2009 and 2011, Ofcom's report has concluded.
That report had concluded that the NSA was capable of intercepting every fax, phone call and e-mail in Europe.
King had just revealed that the classified version of the report had concluded "that historically Russians have supported Republicans".
The report had concluded that Baghdad had chemical and biological weapons and was seeking to reconstitute its nuclear program.
Frisch laid out the time line they had pieced together, what the hospital's report had concluded.
By 2009, a British travel-industry report had concluded that "Europe" was such a successful "single, unified" brand in China that individual countries would be wise to put aside pride and delay promoting "sub-brands" such as France or Italy.
