http://college4.nytimes.com/guests/articles/2002/02/18/903268.xml
Then the agents searched a fifth man, Sakhera Hammad of New York, whom the men identified as their second contact, and found an alarming piece of paper. Mr. Hammad had a worker's pass to the World Trade Center dated Sept. 5. Suddenly, the case became a possible terrorist plot.
In a telephone interview on Saturday, Mr. Hammad's father, Peter Hansen, said his son was a plumber, and he provided a letter he said he had obtained from his son's employer attesting to his work at the trade center. In the letter, dated Feb. 13, Sergei Denko, president of Denko Mechanical, said Mr. Hammad had been working for his company in the basement garage area of 1 World Trade Center.
"He was there for a couple of days," Mr. Denko said in an interview. ____________________________________________________
We could ask Mr. Denko who wrote the work order but he will be hard to find. He filed incorporation papers under the alias Sergei Denko, but if you visit the address filed with the State of New York for Denko Mechanical you will find his name is Sergei Davidenko. Additionally, the address given for Denko Mechanical is a residential apartment in an apartment building. Unusual for a plumbing company.
Why does the father have a letter from the son's employer?