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The Office of Justice Programs Convicted Offender
DNA Sample Backlog Reduction Grant Program

Report No. 02-20
May 2002
Office of the Inspector General


According to FBI personnel, state and local laboratory management,17 and the National Commission on the Future of DNA Evidence, several major factors have influenced the productivity of DNA laboratories across the country. Consequently, if a laboratory's productivity cannot keep pace with analysis demand, a backlog of samples awaiting analysis occurs. The following list focuses on those general factors that affect a laboratory's ability to analyze incoming offender samples.

DNA Technology

Three different DNA processing methods have been available to DNA laboratories: the Dot Blot method, the Restriction Fragment Length Polymorphism (RFLP) method, and the Short Tandem Repeat (STR) method. All these methods work on a similar principle - the process focuses on areas of the DNA that are very different from one person to the next. These areas are considered junk DNA because they do not "code" for anything (i.e., the DNA does not translate into a personal identifying characteristic like "blue eyes" or into a genetic predisposition for disease).

The Dot Blot method is the least discriminating of the three methods. The results of the method are not used for comparison in CODIS databases, and therefore, no further information is included on this method.

The RFLP method is very discriminating but requires large amounts of good quality DNA and is the most time-consuming method; therefore, laboratories using this method will not have the same productivity level as a laboratory using STR. The RFLP process basically takes a DNA strand, looks for a certain combination of molecules on that strand, cuts the strand at that spot (locus), and then measures the length of the resulting fragments. A DNA strand looks like a ladder and RFLP measures the fragments by counting how many "rungs of the ladder" (called base-pairs) are in each fragment. Each person has these loci, but the variation between people is the length of the fragments.

The STR method is also very discriminating, but unlike RFLP can use small amounts of DNA and degraded DNA. In addition, the STR method can be done in a matter of days rather than weeks. The STR process is similar to RFLP, but the loci it looks at are different and the measuring unit it uses is different. STR looks for sections of repeating combinations of molecules, cuts the strand after the section of repeats, and then measures how many repeats were in that section.

Unfortunately, the results from RFLP analysis and the results from STR analysis are not compatible. Therefore, laboratories that have a well-established RFLP program and switch to STR face the trouble of not only getting different equipment and materials, perhaps changing the layout of their laboratories, and re-training all their staff, but also face the daunting task of performing STR analysis on all the DNA samples previously tested with RFLP.

Therefore, a laboratory's productivity and ability to deal with incoming convicted offender samples will depend greatly upon which method the laboratory has been using and whether that laboratory had to switch from RFLP to STR.

Potential Resource Issues

A laboratory's ability to keep pace with incoming convicted offender samples is greatly affected by resource issues. Examples of resource issues include:

State Legislation

State legislation issues are discussed in detail in the Introduction section of this report, and unfunded mandates are covered by the Funding section above. These legislative issues combine to provide a challenging environment in which convicted offender databasing laboratories must work, and an environment that may not permit a productivity level that keeps pace with incoming samples.

Role of Sample Collection Agencies

Various agencies external to the laboratory are often charged by the legislation to oversee the collection of the convicted offender samples and the safe transfer of those samples to the possession of the laboratory. These agencies can include prison facilities, local jails, sheriff's departments, and probation and parole offices. These external agencies face similar hurdles as the laboratory, including limited resources, unfunded mandates, and political issues. Also, the collection process makes the laboratories dependent on accuracy and thoroughness on the part of these external agencies. The collection agencies must ensure that the correct people are giving samples and that full and accurate identifying and criminal history information is sent to the laboratory with the sample.

  1. Interviews with FBI personnel and state and local laboratory management were conducted during the OIG internal audit of The Combined DNA Index System, Report No. 01-26. In addition, auditor observation during the eight CODIS Laboratory Audits conducted as a part of that internal audit were factored into the points that follow.