The following is a quote from "The Anguish of the Emperor and Hideki Tojo" by Michio Shiota as this is the most reliable source at the moment.
"It was about an hour and a half before all the remains were burnt.
When the incinerator door was opened and the ashed remains were removed with a long iron poker, the crematorium chief Tobita allocated some of the remains of the seven executed men into seven urns and hid them elsewhere. However, these hidden urns were found by a US guard because he noticed scented smoke of incense sticks which probably someone placed to mourn and had been moved to the US hands. These remains were thrown into an iron bowl and stabbed with something like an iron bar to be crushed into small pieces. It was just a ruthless act of whipping the dead. There was a rumor that the US military would crush the remains of class-A war criminals and scatter them from the sky into Tokyo Bay in fear of them becoming an object of hero worship.
Tobita who failed to hide the remains was with uneasy impatience. After crushing the remains, US soldiers took out seven black boxes and put the remains into them to write the numbers from 1 to 7 on them. These boxes were brought away by the US soldiers who brought in the bodies from Sugamo. The small bone fragments and ashes left on the table were ordered to be thrown into the communal bone dump in the crematorium under the supervision of US guards.
Taking back the remains was planned by Lawyer Shohei Sanmonji who was the defense counsel for General Kuniaki Koiso at the Tokyo War Crimes Tribunal. Sanmonji consulted with US lawyer Bruwet in advance to ask GHQ handing over the remains to their families. However, Gen. MacArthur did not admit at all. Then, Sanmonji learned that the remains would be cremated at Kuboyama after executed at Sugamo Prison.
Sanmonji visited Kozenji Temple which was located there just above the crematorium to meet the chief priest Iyu Ichikawa. Abbot Ichikawa was also one of those who went to the Tokyo Tribunal to hear and was angry at the unfairness of the trial. Sanmonji asked Ichikawa for cooperation enthusiastically "If the remains of those class-A war criminals were not returned from the hands of US military, our people would admit the result of the unfair Tokyo trial and even the three million spirits who were driven to the battlefield by their orders would be humiliated and disappeared." Abbot Ichikawa was also intolerable as a Japanese, so he undertook to cooperate with Sanmonji. He introduced Tobita as the crematorium chief to Sanmonji.
With help of people working in the Kuboyama Crematorium, the remains of class-A war criminals could be hidden separately at first but found out by a US guard. This time, the remains which had been abandoned in the communal bone dump must be taken out. Until the next new remains were thrown in, these remains of seven victims would be left as they were although some other unrelated fragments were mixed in. They decided to recover them on the night of December 25th when U.S. military's attention would be loose on the Christmas.
When it got dark, Lawyer Sanmonji and the chief priest Ichikawa sneaked into the crematorium's bone dump guided by the crematorium chief Tobita. In the darkness, three men wore cloaks from their heads and crouched down to begin work so that they could not be found by US guards. The three patiently groped for the remains so as not to make noise. Although the remains of the seven were part of the whole, they were able to collect a full pot in a large urn.
The remains recovered from the crematorium were reburned to remove moisture. If this event was leaked to the world, they would be blamed by the US military. So, Sanmonji remarked the name of his nephew Shosuke Sanmonji who died in the Battle of Shanghai on the urn. Secret memorial service for the seven was to be held at Kozenji Temple for some time.
("The Anguish of the Emperor and Hideki Tojo" by Michio Shioda 「天皇と東条英機の苦悩」塩田道夫 三笠書房 1989) "
Source:
天皇皇后両陛下による七人の士への墓参り | ひろぶーログ
Lawyer Shohei Sanmonji
Source:
お墓のはなし | 合資会社 宮田石材商会 ｜ 創業300年の信頼と実績