Vice Transport Minister Hisashi Umezaki admitted Monday that his ministry did not secure an airport security "blind spot" pointed out by the man arrested Friday for hijacking an All Nippon Airways jumbo jet and killing its pilot.

The 28-year-old resident of Tokyo's Edogawa Ward allegedly hijacked ANA Flight 61 bound for Sapporo from Tokyo's Haneda airport shortly after takeoff Friday morning and stabbed Capt. Naoyuki Nagashima with a 20-cm knife he carried onto the plane.

In a letter sent to the Haneda airport authority late last month, the man detailed how passengers could circumvent X-ray monitors to sneak weapons onto a plane.

"(After receiving the letter), we immediately did what we could. But there is no doubt our measures were insufficient. Although we kept examining possible countermeasures against what the suspect pointed out, we were not fast enough," Umezaki told a regular press conference.

Under the current security system, X-ray monitors are used to examine carry-on bags before passengers board planes, but inspectors do not X-ray luggage at the departure counter.

Prior to boarding the ANA flight to Sapporo, the alleged hijacker flew round-trip between Haneda and Osaka, checking in a bag containing the weapon.

Upon returning to Haneda, the man retrieved the bag from the baggage claim area, extracted the knife, and used a "staff only" passage to get to the departure lobby for the Sapporo flight.